Raise Event on another Form

EngrImad

Hello everyone subject is declare event on Form1 , and run that event on Form2 here is the code , but event doesnt work on Form2 !! what is missing here?? many thanks

Public Class Form1

Private Sub btnOpenForm2\_Click(sender As Object, e As EventArgs) Handles btnOpenForm2.Click
    Form2.Show()
End Sub

Public Event show\_My\_Message()
Private Sub btnShowMessageOnForm2\_Click(sender As Object, e As EventArgs) Handles btnShowMessageOnForm2.Click
    RaiseEvent show\_My\_Message()
End Sub

End Class

Public Class Form2

Public WithEvents My\_Form1 As Form1 = New Form1
Private Sub Show\_My\_Message\_On\_Form2() Handles My\_Form1.show\_My\_Message
    MsgBox("Hello")
End Sub

End Class

Dave Kreskowiak

What you're doing seems backwards, but, hey, it's your app and I don't know anything about it. Since Form2 doesn't (and SHOULDN'T!) know anything about Form1. By doing this, you forever tie both forms together making it impossible to use one of them without the other. Your Form2 code is creating a NEW INSTANCE of Form1, NOT using the existing instance! That's why it doesn't work. You do not need the "WithEvents", or even that entire line, on Form2. If Form2 needs to subscribe to events exposed by Form1, you have to pass your instance of Form1 to a constructor on Form2 so it knows which instance events to subscribe to. Then the constructor needs to "wire-up" the event handlers for whatever events it needs, manually using AddHandler. My VB.NET is really rusty, so the following may not even compile let alone run:

Public Class Form1
Public Event Show_My_Message(ByVal message As String)

Private Sub btnOpenForm2\_Click(sender As Object, e As EventArgs) Handles btnOpenForm2.Click
    Dim form2 As New Form2(Me)         ' This passes the reference to the Form1 instance to the Form2 instance
    form2.Show()                       ' Show an instance of Form2
End Sub

Private Sub btnShowMessageOnForm2\_Click(sender As Object, e As EventArgs) Handles btnShowMessageOnForm2.Click
    RaiseEvent Show\_My\_Message("Some message")
End Sub

End Class

Public Class Form2
Public Sub New(Form1 eventProvider) ' THIS IS BAD PRACTICE! Form1 should be replaced by an interface!
AddHandler eventProvider.Show_My_Message, AddressOf ShowMyMessageHandler
End Sub

Public Sub ShowMyMessageHandler(ByVal message As String)
    MsgBox(message)
End Sub

End Class

Asking questions is a skill CodeProject Forum Guidelines Google: C# How to debug code Seriously, go read these articles.
Dave Kreskowiak

jsc42

I've never got along with Events - they seem overly convoluted for simple tasks. My (also) rusty VB suggests that something like the following might do what you want (it is probably overkill)

Public Class Form1
Private f2 As Form2 = Nothing

Sub F2IsActive(Enabled As Boolean)
    btnStartForm2.Enabled = Not Enabled
    btnDoSomethingOnForm2.Enabled = Enabled
    btnCloseForm2.Enabled = Enabled

    If Enabled Then
        If Not FormIsOpen(f2) Then  ' Needs to be opened
            f2 = New Form2()
            f2.Show()
        End If
    ElseIf FormIsOpen(f2) Then   ' Needs to be closed
        f2.Close()
        f2 = Nothing
    End If
End Sub

Private Sub btnStartForm2\_Click(sender As Object, e As EventArgs) Handles btnStartForm2.Click
    F2IsActive(True)
End Sub

Private Sub btnDoSomethingOnForm2\_Click(sender As Object, e As EventArgs) Handles btnDoSomethingOnForm2.Click
    If f2 Is Nothing Then
        MsgBox("You have to open Form2 first")
    ElseIf FormIsOpen(f2) Then
        f2.DoSomethingOnForm2()
    Else    ' No longer exists
        MsgBox("Form2 has disappeared")
        F2IsActive(False)
    End If
End Sub

Private Function FormIsOpen(formToFind As Form) As Boolean
    For Each testform As Form In Application.OpenForms
        If testform.Equals(formToFind) Then
            Return True
        End If
    Next

    Return False
End Function

Private Sub btnCloseForm2\_Click(sender As Object, e As EventArgs) Handles btnCloseForm2.Click
    If Not FormIsOpen(f2) Then
        MsgBox("Form2 has already been closed")
    End If

    F2IsActive(False)
End Sub

Private Sub Form1\_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    F2IsActive(False)
End Sub

End Class

Public Class Form2
Public Sub DoSomethingOnForm2()
MsgBox("Hello from Form 1")
End Sub
End Class